fcm make: build: fix etc files install

The configuration line `build.prop{class,file-she.script} = #!`
generated by the mirror step is causing the build of etc files to behave
incorrectly. This change hard codes `#!` in the pattern match. (It is
standard Unix, so is unlikely to ever change.)

In any case, the `build.prop{file-she.script}` is actually not a documented property.